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their motion. With this object also it is almost invariably the practice here, to employ an independent wheel to drive the paper machine alone.

Some attempts have recently been made in this country to regulate endless paper machines by the second method, and accordingly "pulp regulators" have been applied with considerable success in several important mills.

İt being, in fact, a desideratum to procure some unobjectionable means of effecting the regulation referred to, we have translated below, for the benefit of our readers, from J. B. Viollet's "Journal des Usines," (Journal of the Workshop,) an account of a mechanical contrivance devised in France for this object. Сом. Рив.

Regulator for feeding machines making Endless Paper: by Messrs. SANDFORD, and VARRALL, Mechanical Engineers of Paris.* Whatever care may be taken to render uniform the speed of the motors which drive endless paper machines, and notwithstanding we usually establish for each of these machines a separate water-wheel, constructed of iron, in the best provided works, it has long been impossible to obtain a regularity of motion, and a harmony between the movement of the endless cloth, and the feeding on of the pulp, so that the paper may possess uniformly the same thickness.

From this resulted a serious imperfection, consisting of a marked inequality between the different parts of the long band of paper, and, consequently, between the sheets into which it is cut. We conceived that this inequality was not only a fault, but also that it exposed the manufacturers to disputes not arising from any fault on their part.

In fact, to cause the velocity of the machines, and, consequently, the strength of the paper to vary, it was enough that the resistances op

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These inventors have taken out (April 18th, 1841,) a French patent for ten years, for this eminently useful apparatus, which they and their successors, Varrall, Middleton & Elwell, have applied, at the present time, to their fine machines for the manufacture of paper.

posed by the materials were not constant, or that the stream of water happened to be disturbed.

It is to avoid these difficulties and inconveniences that Sandford and Varrall have invented the apparatus represented in figures 1, 2, 3, 4, 5, and 6, of which their successors have had the kindness to allow us to take off the details in their workshops.

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This apparatus consists principally of a wheel, R, provided with a certain number of scoops, e, which take up the diluted pulp, elevate it, and pour it into a receptacle, from which the filter, c, conducts it into the vat for working the paper machine. The motion of the wheel, R, being connected both with that of the water-wheel, and of the endless cloth, it is easy to see that if the receiver accelerates, or retards its motion, in consequence of some variation in the level, or quantity, of the water above, the rapidity of the revolution of the scoop wheel, R, and the motion of the endless cloth of the machine, will each feel a proportional variation. But as the scoop-wheel for each of its revolutions pours the same quantity of pulp into the filter, C, of the machine, it is evident that the feeding on of the pulp will augment, or diminish proportionally to the velocity of translation of the endless cloth, and that, consequently, the strength of the paper ought to be constant, so long as we do not change the ratio between the quantity of pulp furnished, and the distance moved in a given time by the metallic cloth.

This principle established, let us make known the details of the ingenious apparatus of Sandford and Varrall.

R, as we have said, is the regulating wheel, provided with scoops, e, e, e; this wheel is confined in a drum, B, which the pulp enters from the reservoirs, A, A, by the large stop-cocks, r, r, kept entirely open, so as to maintain sensibly in the drum, B, the same level as in the reservoirs, A, A. It is of little importance, moreover, if this level be not rigorously equal, nor even if it varies notably in the reservoirs, A, A; for, provided the pulp arrives in sufficient quantity, and we must take care that it be always so, each of the scoops, every time they issue from the pulp, only withdraws the same quantity of material.*

We easily conceive how advantageous is this property of the apparatus, since, notwithstanding all the variations of level of the liquid pulp in the reservoir, or stuff chest, it assures regularity in feeding on the pulp,-a regularity which would often be compromised if made dependent solely on this level.

It is necessary that the relation which exists between the number of revolutions of the scoop-wheel, R, and the velocity of the endless cloth may be varied, when we wish to alter the strength of the paper. To obtain this effect Sandford and Varrall have controlled the scoop-wheel, R, by the two parallel cones, C, and C', which carry the belt, d. The cone, C', receiving its motion from the lateral shaft established along side the paper machine, and on which is all the gearing which moves the endless cloth, and the other movable parts of the machine.

It is sufficient to move the belt laterally, (along the cones,) in order to retard, or accelerate the rotation of the scoop-wheel, without altering the angular velocity of the other movable parts, and thus, consequently, to change the relation in question, and of course the thickness of the paper made.

The velocity is never so great that the influence of variations in the centrifugal force need be taken into account.

This displacement of the belt, d, is effected with great facility, by means of a fork, or shifter, f, mounted on a screw, v; this screw carried by the standards, S', S', is moved through bevel geer by the hand-wheel, p, which answers as a handle to manage it. The fork,

or shifter, f, remains fixed, and, consequently, maintains the belt in the same place always, until we move the hand-wheel, p.

This useful apparatus appears to us to be an indispensable adjunct to all paper machines, of which we desire the products to possess with certainty, that uniformity which is so desirable, or rather so necessary.*—(Journal des Usines.)

On Coal-Gas. By THOMAS THOMSON, M. D., F.R.S. L. and E., M.R.I.A., Regius Professor of Chemistry in the University of Glasgow.

There are four varieties of coal which have been tried in Great Britain in the manufacture of gas, namely, caking coal, cherry coal, splint coal and cannel coal. Of these the cannel coal, or parret coal as it is called here, yields the best gas; the caking coal, or Newcastle coal, yields the worst, and the cherry and splint, though very different in their appearance, yield an intermediate gas, the quality of which, whether from cherry or splint coal, is nearly the same.

There are three varieties of cannel coal in the neighborhood of Glasgow, named from the localities where they occur, Skaterigg, Lesmahagow and Monkland.

The specific gravity of these varieties of coal is as follows:-
Caking coal. . 1.280 Mr. Richardson.

Cherry coal.

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Besides ashes, these six varieties of coal consist of carbon, hydrogen, azote and oxygen, combined in various proportions according to the coal. I shall here give the composition of each; that of the first three was determined by Mr. Richardson of Newcastle in the laboratory at Giessen; that of the last three in the College laboratory by Dr. R. D. Thomson. The azote is small in quantity, so small that Mr. Richardson did not succeed in determining its exact quantity; but we found no difficulty in coming to very exact conclusions by the process of Will and Varrentrapp.t As the quantity in all our varieties tried varied from 1-48 to 1.75 per cent., I have supposed that the azote in the three varieties determined by Mr. Richardson was the mean of these two quantities, or 1.61 per cent. The following table shows the composition of these coals.

*We cordially agree with M. Viollet, in his commendations of this ingenious and desirable machine, and recommend it to the notice of paper makers in this country. COM. PUB. + This process was first proposed by Dr. Schafhaeutl, in Phil. Mag. [S. 3. vol. xvi. p. 44.]

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It will facilitate our conception of the composition of these different coals if we exhibit their condition by empirical formulas representing the atoms of each constituent, the quantity of azote being reckoned one atom: we leave out the ashes, because they have nothing to do with the production of the gas, excepting that they materially influ ence its quantity.

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Skaterigg

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C102

46

9

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52

14

Lesmahagow C Н. Az 0,
110
Monkland . C111 H3 Az 018
C111 53

It appears from this table that Newcastle coal contains the most carbon, and Monkland cannel coal the least; while cannel coal contains the most oxygen and Newcastle coal the least; Newcastle coal contains the least hydrogen and cannel coal the most. Now cannel coal yields the best and Newcastle coal the worst gas. This need excite no surprise; carbon not being volatile, it is obvious that if coal contained nothing but carbon it would yield no gas at all. Coal-gas is a mixture of four different gases, most of which are compounds; two are compounds of carbon and hydrogen, one of carbon and oxygen, and the fourth is pure hydrogen. There is no difficulty in conceiving the formation of the gaseous compounds of carbon and hydrogen, but it is not so easy to explain the occurrence of carbonic oxide and hydrogen. These two gases are never entirely wanting; at least I have analyzed above forty specimens of coal-gas from different kinds of coal and from different gas-works without ever failing to find them. I think it probable that they make their appearance towards the end of the process of heating the coal. It is well known that the longer the process of gas making is continued, and the higher the temperature at which the gas is produced, the worse is the gas, and of course the more hydrogen it contains. Is it not possible that coal may contain water; that this water can only be extricated at a high temperature; that its oxygen combines with carbon and forms carbonic oxide, while the hydrogen makes its escape in the gaseous state?

If this supposition were true, there ought to be a constant ratio between the volume of carbonic oxide and hydrogen in the coal

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